1. Field of the Invention
The invention relates to photocurable compositions, more particularly to photocurable compositions for stereolithography.
2. Related Art
U.S. Pat. No. 5,002,854 to Fan et al. discloses a photohardenable composition for stereolithography containing filler particles that are core shell polymers. The core is a crosslinked multifunctional ethylenically unsaturated monomer; the shell is based on a monofunctional ethylenically unsaturated monomer. The particles are non-reactive and do not chemically bond to the polymer matrix formed on curing the composition.
U.S. Pat. No. 5,461,088 to Wolf et al. discloses a stereolithography formulation containing a polysiloxane block copolymer that is added to the formulation as an oil or crystals. The block copolymer is not a core-shell polymer and contains no reactive epoxy groups or ethylenically unsaturated groups. U.S. Pat. No. 5,463,084 to Crivello et al. discloses a photocurable composition containing silicone oxetane monomers that are liquid. U.S. Pat. No. 5,639,413 to Crivello discloses a photocurable composition containing a cyclohexylepoxy siloxane monomer that is liquid.
3-D objects made by stereolithography are generally clear or slightly hazy, and tend to have rough surfaces. Opaque white objects with smooth surfaces are desirable as similar to plastic objects made by non-stereolithography processes. Smooth sidewalls are especially useful when using an object prepared from stereolithography as a model to prepare a mold. There is therefore a need for alternative photocurable compositions for stereolithography to allow for variation in color, opacity, and surface properties. In particular, there is a need for stereolithography compositions that form opaque white or colored objects with improved surface properties.
In stereolithography, the usual way of producing opaque materials is to add fillers: fillers will often settle out over time and their incorporation into photopolymerisable composition generally requires the composition to be repeatedly homogenized, e.g. by stirring.